Biological membrane deterioration and associated quality losses in food tissues

Biological membranes are rarely considered by food scientists when the deteriorative reactions that take place during the processing or storage of food tissues are studied. Yet, membranes and their deterioration play a major but underestimated role in food losses, and recent biochemical information indicates that at least some of these reactions can be controlled by procedures suited to food materials. Much of the present information available on membrane degradation in food systems is incomplete and speculative. It is known, however, that in order to accomplish their many indispensable functions in cells, membranes are constituted mainly of phospholipids, protein, and some carbohydrates arranged in thin, bimolecular sheet-like structures that serve to compartmentalize cells and their organelles. Membranes have embedded in their asymmetric surfaces complements of catalytic and cytoskeletal proteins that serve permeability and structural functions. Membrane surfaces exhibit fluidity, due partially to the continuous lateral diffusion of lipids and some proteins. Two important consequences of fluidity are the ability of membrane phospholipids to exist in different interconvertible conformational phase structures and the formation of heterogenous lipid domains on the membrane surface. Cellular death leads unavoidably to the initiation of membrane deterioration. While the time course of this series of reactions differs in animal and plant tissue, they are damaged by generally similar mechanisms. These include an initial peroxidative attack on polyunsaturated fatty acids, with the concomitant production of free radicals. Many biological agents can act as accelerating agents in these reactions, including transition metal ions, heme compounds, radiation, illuminated chlorophyll, calcium, and ethylene. Once formed, free radicals catalyze further reactions that can affect all aspects of membrane function and cellular metabolism, and lead ultimately to significant losses in food quality through defects such as chilling injury and cold shortening. These are aggravated by many food-processing steps, especially those that involve tissue disruption. Control of membrane breakdown by exogenous chemical intervention has been practiced, but, at best, this only slows the rate of these reactions. Newer approaches to this problem include dietary treatment of meat animals, modified storage and packaging conditions, and genetic interventions. This review advances the proposition that membrane deterioration can be considered a "universal mechanism" that leads to significant quality losses in food. Perhaps because the study of biological membranes and the biochemical and physiological properties has only begun recently, not much progress has been made in finding practical control mechanisms for these reactions in food systems.(ABSTRACT TRUNCATED AT 400 WORDS)